Bolt rocker arm assembly slant

SixBanger · Dec 9, 2018

Hello,

Currently I have been busy with the replacement of the valve seals in the slant.
This was easy to do with the help of a valve spring compressor and a piece of nylon wire in the cylinder.

Before I could replace the valve seals, the rocker arm assembly had to be removed.
This went fine. However, I noticed already that the last and longest mounting bolt of this assembly took some iron jacks during disassembly.
Unfortunately, when the rockers were assembled, the damage had already been done. The screw thread was already damaged in the cylinder head.

I saw that this bolt did not look original. Apparently, a replacement bolt has been fabricated and assembled. This bolt is an M10x1.5. I also see that a slot has been made with a grinding tool. Bolt shown in first picture.
My question, is this done as an oil passage for the supply to the rockers and push rods? I have been able to find an image on the internet about how the lubrication runs in the block.

Is it possible to place a helicoil in this specific threaded hole?

Aspen500 · Dec 9, 2018

You are correct about where the oil supply to the rocker shaft comes from. My guess is the slot was cut into the bolt to attempt to make it into a self-tapping bolt to ram a metric bolt into an SAE thread. You can put a Heli-Coil in the hole. The threads of the hole are below the oil passage so just be sure the Heli-Coil is the same way.

On second thought, that bolt looks kind of short. Did they thread the upper part of the bolt hole for this bolt? If so, the groove could be for oil. Normally, the oil goes past the bolt in the larger bore above the threads. I really hope I'm remembering this all correctly, it's still early..............

SixBanger · Dec 9, 2018

Thanks Aspen!

The bolt is made according to me from a threaded rod. Where a nut is fixed. In view of this, the thread would run longer.
Yesterday I could not see very well in the twilight if the top bore was much bigger than the screw thread.
But as you indicate, it seems likely to me that they have made a self-tapping bolt.

I intend to make a fitting M10 bolt of a round bar RVS. But then I do not have to drill a hole to pass oil.

But first, I have to remove the cylinder head to place a Heli-coil and clean it.

Can you reuse the cylinder head bolts?
This is the first time I will get it off. Rack bolts are used in more modern blocks.

volare 77 · Dec 9, 2018

I have reused head bolts on a small block many times without a issue. Would it be recommended probably not. I assume the slant six wouldn`t be much different. Can you put a stud in the hole? Are the threads in the hole completely gone or messed up? Does the head really need to be removed? Can you plug the oil feed hole below and then tap the hole or would the debris cuttings get in the oil feed? According to my parts book the bolt was 5/16 x 2 1/4 which would be longer the the other hold down bolts. Does that sound correct? The original bolt would not be metric BTW. It seems to me someone put a shorter bolt in the hole and stripped it out but if the bolt was 2 1/4 long then maybe there is still enough threads for a stud. Just thinking out loud.

SixBanger · Dec 9, 2018

Hey volare 77, thanks for your response. Good to hear that the bolts can be reused.

I can not see how the state of the wire is right now. But this would probably be bad, the bolt does not hold a momentum.

I was also watching if the head did not need to be removed. The relevant hole is at the very rear of the cylinder head. I think you get in the way with a tap and the frame of the car. In addition, it would be guessing whether the Heli-Coil and tap gets right.
I also have a complete engine gasket already.

volare 77 · Dec 9, 2018

ok, I haven`t worked on a slant in a long time so I wasn`t sure. I edited my previous post while you where responding asking whether the threads are deep enough on that hole to hold a stud. The bolt you show looks shorter then 2 1/4 assuming the size in the parts book is correct. A 5/16 bolt would be closer to a 8 in metric. So I think the hole is larger at the top to allow for the oil flow and the actual bolt hole was 5/16 and someone put in the larger bolt and cut the slot not knowing the top wasn`t stripped but it was made that way. Assuming the bolt hole has a bottom you could stick something in the hole and see how deep it is. Unless of course if the whole problem is that someone broke the bolt off and it is in the bottom of the hole. If so, then because of what you said about not having room you probably will have to remove the head anyways.

SixBanger · Dec 9, 2018

Ah right. Thanks to know the original dimensions of the bolt. I assumed that the original builds a 3/8, but good to know it isn't. May I ask how you came to the parts book?
Yes the bolt is shorter, 46mm (1.8 inch). Tomorrow I would check the depth of the hole.

Hopefully the original bolt is not broken. And the remaining depth could still be tap to metric without the use of a heli-coil. Roughly 11 millimeter depth (2 1/4 - 1.8) should be left. With a thread pitch of 1.5 means that the stud can be turned around seven times. I think this should be enough for this?

Tonight I have already disassembled most of the engine accessories. Only disassemble the manifolds before the head can be removed.

volare 77 · Dec 9, 2018

I have a 77 book. All the other rocker shaft bolts are shorter and larger 3/8 x 1 3/4 according to the book. That one bolt is smaller and longer.

SixBanger · Dec 9, 2018

Alright. I would check it.

SixBanger · Dec 12, 2018

I have removed the cylinder head of the engine.

As in the first photo can be seen, the original bolt was broken. This at the level of the oil supply channel.
So I have mounted the head on a milling machine. Centered on the corresponding threaded hole.
The broken bolt came out of the thread-hole quite easily. This with the help of drilling a hole and using a left tap.

The length of the broken piece of wire is around 12 mm. This seems to me sufficient to mount the original bolt (8.5 turns).
I have now ordered a UNC 5/16 x 2.1 / 4 bolt.
Because of this I do not need to tap a metric thread or apply Heli-Coil.

So it would be assembled on the engine soon.

Oldiron440 · Dec 12, 2018

There's no substitute for rewards of doing things correctly, can you here the applause!

volare 77 · Dec 12, 2018

So my guess of a broken bolt was correct. Glad you got it out with ease. It`s a shame you couldn`t get to it while on the car. Also for some reason the parts book had a part number listed for that bolt. It makes me wonder if there was anything special about it. The other bolts didn`t have a part number and were listed as not serviced meaning you can get them at a hardware store or bolt supplier.

SixBanger · Dec 12, 2018

Thanks all for help!

Indeed it would have been nice if I could replace it without removing the head.
But then it remains difficult to drill a hole right in the middle and straight of the broken bolt. Let alone that you can clearly see what you are doing at all.

Strange that the rear bolt has a part number and the other bolts do not. I do not know what the original bolt looked like. But it seems to me a normal hex bolt that can be obtained from a bolt supplier like I did.
Or it appears to be more common that these break down?

Or does this bolt have an adaptation for the supply of the oil? The hole above the wire end is about 10 mm, and the bolt around 8 mm. Seems sufficient space for the flow of oil.

Aspen500 · Dec 15, 2018

That is more than sufficient for oil passage to the rocker pivots.
My '79 parts manual says the same thing. P/N for the rear bolt and the others it only gives a dimension (3/8" x 1 3/4") and says "not serviced". It does seem kind of strange they'd do it that way.

SixBanger · Dec 16, 2018

Alright! Tnx

Charrlie_S · Dec 16, 2018

Early slants, had a 3/8 bolt in the rear location. Later on (can't remember what year) they changed the bolt to a special one. 5/16 dia, with a larger dia, at the top, and changed the hole in the rocker shaft, so the shaft can only be installed one way. The hole in the rocker shaft is larger at the top, and smaller at the bottom. The later rocker shaft can be used on the early heads by drilling the lower rear hole larger. The early shaft can be used on the later heads with no changes, just need to make sure the shaft is installed in the correct orientation (rocker oil holes down, and toward the valve springs).
PS: there is supposed to be a flat ground on the top front of the shaft, as an indicator, but it is sometimes hard to see. The stock late shaft, and bolt combination cannot be installed incorrectly.

Bolt rocker arm assembly slant

SixBanger

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Aspen500

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SixBanger

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volare 77

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SixBanger

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volare 77

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